Apparatus for treating dental investments



April 1930- R. v. WILLIAM s 1,756,325

APPARATUS FOR TREATING DENTAL INVESTMENTS Filed March 19, 1926 M alum Patented Apr. 29, 1930 ATENT OFFICE REGINALD V. WILLIAMS, OF BUFFALO, NEW YORK APPARATUS FOR TREATING DENTAL INVESTMENTS Application filed March 19, 1926. Serial No. 96,094.

This invention relates generally to a vibrator but more particularly to a method and apparatus for use by dentists and dental mechanics when pouring the standard dental refractories or investments into a flask or mold.

One of its objects is to provide a simple and inexpensive vibrating apparatus for this purpose which will gently and effectually remove any trapped gas or air bubbles from the investment contained in the flask.

Another object of the invention is to provide an electrically operated dental vibrator which is durable in construction, which is not liable to get out of order, and which is easily adjustable to vary the intensity of the vibration for various kinds of work.

In the accompanying drawings:

Figure 1 is a sectional side elevation of the dental vibrator constructed in accordance with my invention. Figure 2 is a top plan view thereof. Figure 3 is a transverse section thereof on line 3-3, Fig. 2. Figure 4 is a top plan View thereof with the cover removed.

Similar characters of reference indicate corresponding parts throughout the several views.

The normal procedure of making a dental restoration of gold or other metal by the casting process, consists of taking a wax pattern or impression a of the tooth-cavity, appyling it to a sprue or a metal pin 6 and then placing it in a flask 0 into which the investment material (l is poured to completely surround the wax pattern. This investment material solidifies in a short period of time and the excess moisture is driven out by heat which also dis.- sipates the volatile wax pattern, leaving a cavity in the investment which is an exact reproduction of the cavity-to be filled in the tooth. The metal, usually a gold alloy, is poured in a molten state into the investment cavity and when solidified is placed into the cavity of the tooth.

When preparing the investment, that is, mixing a dry refractory with water, air is present and certain chemical reactions take place whereby gases are evolved, and when this fluid mass is poured into the flask it contains trapped gas or air in the form of small bubbles, which later appear as voids in the set investment adjacent to the wax pattern. Hence, when the gold is poured into the investment-cavity it fills these voids and the resulting casting is not a reproduction of the wax pattern and therefore does not properly fit the tooth-cavity.

My invention consists of an instrument, upon which the flask c is adapted to be placed, capable of removing trapped air and gases from the liquid investment by means of gentle yet etficient vibrations. In the preferred embodiment thereof illustrated in the drawings, the instrument comprises abase or cylindrical casing 10 of aluminum, bakelite or similar material, the top of the casing being open and its bottom having a rubber mat 11 applied thereto. Contained in an upright position in this casing is an alternating current electromagnet having a central core or pole 12 and side poles 13, 13 composed of a series of laminations 14 of soft iron shaped as shown in Fig. 3. Surrounding the central pole and passing through the resulting spaces between it and the side poles is an inductively wound coil 15 having an insulating covering 16. The ends or terminals 17 17 of this coil may be connected to a suitable plug for insertion in an ordinary switch-socket of an alternating current supply line of any commercial frequency. Brackets 18 secured to the opposite upper ends of the side-poles 13 are employed for suspending the magnet from the top of the casing, screws 19 being used for reliably fastening the magnet thereto, as shown in Fig. 4. It will be noted, reference being had to Fig. 3, that the electromagnet is spaced from the side walls and bottom of the casing to provide an'air chamber 20.

Mounted in a more or less vertically free position over the open end of the casing for cooperation with the electromagnet is a cover plate 21 of cast iron. which formsa support for the flask 0 and also constitutes the Vibratory member of the instrument, serving to complete the magnetic circuit between the core and coil of the electro-magnet. Adjusting screws 22, 23 passing loosely through openings 24 in diametrically opposite sides of the cover plate and engaging alining threaded openings 25 in the casing 10 serve .a counter-bore 26 of the corresponding threaded opening 25 is a coil spring 27 whose upper end bears against the underside of the cover plate, as shown in Fig. 1. This spring normally tends to hold the plate elevated away from the electromagnet, in which position the parts are illustrated in the dyd rawings.

The top faces of the si e poles 13, 13 of the electromagnet are substantially flush with the upper edge of the casing 10, while the top face of the center pole 12 is slightly below the corresponding faces of said side poles to provide an air gap 28 between such center pole and the cover plate 21 in its lowered or attracted position. This arrangement focuses the magnetic flux and brings the magnetic strain at a central point where it tends to close the air gap.

In operation, when the customary socketswitch is turned on, a current passes through the coil 15 of the electromagnet and the resulting magnetic attraction causes the vibration of the cover plate 21 in direct ratio to the frequency of the alternating current. Between the changes of the frequency of current, the spring 27 acts to force the plate upward or away from the poles of the electromagnet to complete the vibrating stroke, the

tension of the spring being overcome whenever the current frequency is changed. By adjusting the screws 22, 23, the strength or intensity of the vibrations of the cover plate may be varied accordingly.

When pouring a model or investing a casting in the flask 0, the latter is placed on top of the cover plate and may either be clamped solidly thereto or rest loosely thereon as shown in Fig. 3. When the investment material is poured and the vibrator set in-motion by turning on the switch, all the gas and air bubbles contained in such material or contained by surface tension to the wax pattern a, rise very quickly to the surface of the flask and thence into the atmosphere, thereby eliminating voidsin the set investment and producing a casting which is an exact reproduction of the tooth-cavity.

By setting the cover plate toward or from the electromagnet through the medium of the adjusting screw 22, 23, the intensity of its vibrations may be light or vigorous. When pouring the investment for extremely delicate restorations, only the lightest degree of vibration is used, while vigorous vibrations may be used when forming models of plaster of Paris or any so-called dental stones.

This improved dental vibrator is manifestly simple, compact and inexpensive in construction, and it eflectually removes any trapped air or gases from the investment material in a minimum period of time.

I claim as my invention:

A portable device for removing trapped gas or air from the liquid investment of a dental flask, comprising a casing including. a chamber open at its upper end, an electromagnet housed Within said chamber and rigidly suspended from the top of the casing, said elec-- tromagnet including a central pole and side poles and a coil for carrying an alternating current surrounding said central pole, the upper end of the central pole terminating below the level of the corresponding ends of the side poles, a vibratory cover plate mounted on the open end of said casing over said electromagnet for c ompleting the magnetic circuit,

of frequency of current. 4

REGINALD V. WILLIAMS. 

